Ornate magenta and dark (officially "Twilight's Hammer"): no transmog page, see this link for appearance and list of pieces (bracers and boots missing). This is the only colour which has proper shoulder artwork

There are three basic colours which are unavailable: Green, Purple and blue (officially "White")

There are three other "ornate" colours which are unavailable: orange and brown (officially "Argus Wake") can be seen on Argus Shadow Mage; purple and dark (officially "Dark Strand") used to be worn by a bunch of NPCs, including Dark Strand Adept; silver-grey (officially "White Wake") is a beautiful version of the Argus Wake robe, but in grey with silver scrollwork